There are very many forms of molds, and as many molding techniques, and even as many materials that can be used to mold objects. Almost all molds are hollow and of suitable characteristics to receive a given molding material, which may be anything from a molten metal to a liquid plaster or one of the new plastics. Many such molds, particularly for metals and plasters, have been in use for thousands of years.
Most of the ancient molds have been solid, and most of the materials poured into the molds have been in a liquid form, initially, that later hardened into a solid. Some molds were formed in two or more elements to be separated to release the molded object, but other molds had to be broken away to release the molded object.
Newer molding techniques involve latex rubber or plastics formed over solid forms to be duplicated. Rubber and plastic materials may also be used as the molding material.
Almost all conventional molding is most applicable to relatively small objects; either to copy, or to form for simple shapes which may be solid. Larger units are almost always made hollow, to save material and weight, or to function as containers. These are often poured or pressed between an inner and an outer mold section. Such techniques have been adapted to fairly large statues, containers, and the like.
However, there is almost no known technique for forming very-much larger objects, and particularly very-large containers and the like. The larger the vessel or container, the more difficult and expensive it is to make the mold and to use it. Consequently, most large containers are made by other, slower, more laborious, and more expensive techniques. For example, a solid frame may be made in the shape desired and the molding material laid up, with or without reenforcing, within the frame.
It is therefore an object of this invention to provide a mold for the molding of large, nominally-spherical containers, of almost any size.
It is a further object of this invention to provide a mold that utilizes partially-resilient bladders to define an enclosure and form a container between an inner and an outer layer.